The problem with hurricane stories is that one uses up the adjectives on minor-league storms. Mail-order meteorologists and blow-dry weathermen have been inundating us for so long with evacuation hysteria for mere tropical disturbances -- complete with breathlessly narrated TV images of homeowners buying plywood and flashlight batteries -- that we think we've seen it all before.

We haven't. But we may well see it all before sundown. Because for years truly knowledgeable hurricane experts have been warning us that The Big One is what our coastal communities really need to worry about, and today The Big One is here.

It may well be that New Orleans will dodge another meteorological bullet, as it has for more than 250 years, and once again escape the doomsday scenario that has long haunted the dreams of disaster officials and any Crescent City resident thoughtful enough to listen or read.

But it won't be because Hurricane Katrina is a patsy. Yesterday morning the National Hurricane Center cleared its throat and upgraded Katrina to a Category 5 hurricane -- the designation for storms capable of truly catastrophic damage and deadliness. That, however, wasn't the center's most significant statement. The real news was the center's chilling declaration that, at 902 millibars of internal barometric pressure -- the lowest barometric pressure ever recorded in the Gulf of Mexico -- Katrina was "comparable in intensity to Hurricane Camille of 1969 . . . only larger."

Those of us who lived though Hurricane Camille will never forget it. Camille struck with the force of several hydrogen bombs, altering forever the topography of the Mississippi coast. Its nearly 200-mph winds and 25-foot storm surge exploded concrete buildings and erased entire communities -- then gouged open graveyards and hung corpses in the live oaks like so much Spanish moss. There was a problem for a time telling the storm victims from those already embalmed.

More than 250 were dead before Camille swept up the Mississippi Valley as a tropical storm. Then, three days and 1,000 miles after it hit the coast, it took a right turn over West Virginia and, in some sort of terrifying meteorological joke, dumped 20 to 40 inches of rain in eight hours on Nelson County, Va., hosing away entire mountainsides, drowning or burying 150 more people and touching off 100-year-record floods in the James River basin.

Katrina, the National Hurricane Center said, is capable of more. Yet for a true New Orleans doomsday scenario, the storm's eye and strongest winds will have to thread a fairly precise path that carries its deadly northeast quadrant just east of the city. The real vulnerability of the city is not just that it's 10 to 15 feet below sea level, laced with more drainage canals than Venice, and must pump for its life around the clock in even the driest weather. Nor is the city's biggest problem the flown-in TV reporter's favorite specter of a hurricane storm surge up the Mississippi River that overtops the city's famous levees. That could theoretically happen, but it's less likely.

The real nightmare has always been the prospect of a Wagnerian hurricane like Katrina coming ashore so that its strongest winds push the Gulf of Mexico into the eastern-facing entrance to Lake Pontchartrain, which borders the city's northern edge. The lake is both unusually shallow -- rarely more than 20 feet deep -- and unusually large -- more than half the size of the state of Rhode Island. A 20-foot storm surge arriving in concert with both high tide and 20-inch rains could overwhelm the city's more vulnerable lakeside levees and then flow downhill all the way to the French Quarter. Many of the city's massive drainage pumps are located closer to the lake. Were they to be flooded out, the city would not only be helplessly inundated while the hurricane is overhead -- it would remain so for weeks if not months.

For more than 2½ centuries, that precise scenario has never quite happened, though hurricanes rake the Louisiana/Mississippi Gulf Coast regularly and sideswipe the Big Easy more often than not. One reason it hasn't is that the city was long protected by scores of miles of surrounding saltwater marshes capable of sponging up even massive storm surges like a swampy dishrag.

But for the last half of the 20th century and into the present day, those wetlands have been disappearing -- hundreds of acres of them every year -- starved by levees from the Mississippi River overflows that once fed them with silt from Minnesota and Iowa and Missouri, and eroded by canals dug for oil exploration and suburban subdivisions. To compare a 1930 aerial portrait of Louisiana with a contemporary satellite picture is to realize with stunning force how hundreds of miles of the state's beautiful if mosquito-laden southern wetlands now resemble moth-eaten lace.

With a far smaller marshland buffer zone to suck up Katrina's ferocious storm surge, New Orleans is very definitely in harm's way. Never mind the roof-ripping winds. Water fed New Orleans with commerce most of her life. If she dies today, it will be water -- born of Katrina's catastrophic power -- that's the death of her.